Orofacial clefts are among the most common congenital defects in the United States, affecting roughly 1 in 600 births annually. A majority of these cases are considered to be “isolated” clefts of the lip and/or palate (ICLP). However the term “isolated” is somewhat of a misnomer, as functional deficits frequently accompany ICLP. One of the most problematic yet understudied of these deficits involves the high prevalence of reading disabilities in this population. It has been estimated that as high as 46% of children with ICLP will be diagnosed with a reading disability, particularly dyslexia. Despite this high prevalence and the well-established neurological basis of dyslexia, relatively little attention has been paid to the role that brain development plays in the reading problems in ICLP. Previous studies from our lab have demonstrated significant changes in brain structure in children with ICLP (that have importantly correlated with functional measures). However we have yet to combine both a structural and functional neuroimaging study with an in-depth analysis of reading dysfunction in this population.
The current study examined boys with ICLP, age 8-12 (boys have a higher prevalence of ICLP and show more significant reading problems that girls with ICLP) compared to healthy control boys. Measures of cognitive functioning were obtained with an emphasis on reading and language skills. In addition MRI scans were obtained which included volumetric measures, diffusion-weighted measures (DWI; white matter), and connectivity measures (resting-state fMRI). Even after controlling for the effect of socioeconomic status, boys with ICLP showed significant decreases in reading and language skills (particularly reading fluency). Boys with ICLP did not show significant differences on phonlogical measures (the primary cause of dyslexia). In addition, phonological measures were not predictive of reading fluency, while object naming tasks were predictive of reading fluency in boys with ICLP.
For white matter integrity, measures of fractional anisotropy (FA) were found to be increased in the right occipital lobe for boys with ICLP indicating more organized white matter in this region. This increase in right occipital FA was also predictive of better reading outcomes, particularly reading fluency. For more specific white matter tracts, only the fornix and the tapetum (both associated with the temporal lobes) showed a significant difference with a decrease in FA for boys with ICLP. The decrease in FA in the tapetum was also predictive of better reading outcomes in ICLP. When looking at resting-state networks, boys with ICLP showed an increase in connectivity within posterior and subcortical regions when compared to healthy control boys, indicating stronger network connections within the posterior language regions of the brain.
Taken together, these results point to differences in both structural and functional connectivity in the brains boys with ICLP. Furthermore, this pattern is different than that found in children with developmental dyslexia as there appears to be no disruption of the posterior reading systems. Cognitive measures also indicate normal phonological awareness in this group, further distinguishing them from dyslexic children. Boys with ICLP instead may be over-relying on these posterior, more visually oriented reading systems as a compensatory mechanism to overcome problems with the development of the typical “lexical route” of reading.